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Service Engine Soon and odd gas gauge behavior

3 fills ago, my 2005 Nissan Frontier started exhibiting strange indicator behavior. The gas gauge was a little over half full, and I stopped to fill up. Shortly after leaving the filling station, I noticed that the gas gauge needle was pegged low and the low indicator light was lit. Since I knew that I had just filled up I continued on to work. After getting to work, I parked the truck and removed the gas cap. When I checked indications, the gas gauge was back to the level it was before I filled up but the “Service Engine Soon” light was on solid. I checked the manual and it stated that this indication could be an emissions control problem or simply a problem with the gas cap. It said that if it was the gas cap, the problem would go away over the next few trips. On the drive home, the gas gauge indication slowly increased until it indicated full. The next time I got into the car the “Service Engine Soon” light was out and I thought, “problem solved.” It was, until the next time I filled the tank. That time, the gas gauge didn’t do anything, but the “Service Engine Soon” light came on and stayed on for a couple of trips. The last fill, which was yesterday, the “Service Engine Soon light” came on and the gas gauge pegged low with the associated light being lit. I’m pretty sure that the “Service Engine Soon” light could be a problem with the gas cap since it only comes in when the cap is removed, but the behavior of the gas gauge is a bit puzzling and I was wondering if it could be related to the “Service Engine Soon” light. The Frontier currently has about 75,758 miles on it. I haven’t had the code checked, but will try to get that done my next day off.

A new gas cap is cheaper than any mechanic so it might be worth a try, especially if there is any reason to think it might not be seated properly.

Leaving your engine running while filling can do some weird things. I presume this is not the case.

Barkydog: You’re correct, the engine was not running during any of the fills. Any previous ones, either. Good thought though.

The fuel level unit is an input to the Engine ECU and can illuminate the check engine light if a fault is detected. When the fuel level is low the ECU may not run certain monitors therefore it relies on the fuel level unit as an emission control device.

Have the fault codes checked.

Refer to Nissan service bulletin # 07-069D;

The fuel gauge is erratic, inaccurate, or inoperative.

And/Or

The MIL is “ON” with DTC P0461, P0462, or P0463 stored in Self-Diagnosis.

ACTIONS:

Replace the fuel level sending unit with the one from the Parts Information section of this bulletin.

Thanks Nevada_545. That makes sense. If I understand correctly, if the fuel level unit is flaky, which it is, it should illuminate the check engine light. The weird thing is that of the 3 fills, once the gas gauge appeared to be operating correctly. It’s likely that it just didn’t do something I caught, but still malfunctioned somehow. Again, thanks. It makes much more sense now.

Sometimes an open circuit can occur at a paticular fill level, then function normally at other levels.
It is common enough of a problem for Nissan to issue a service bulletin and some 2006 models had a recall issued for this.

That would explain why it happens when I fill up, and it goes away as the level gets lower.

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

I have the same problem with the gas gauge on my '08 Frontier. The dealer said there is a recall on the sending unit and they will fix it for free. Just make sure that the tank is really next to empty when you bring it in because the tank has to be removed to fix it. I plan to do this in the next month or so. Meanwhile, I have an evaporative emissions code coming up as well that needs to be fixed and that’s not under warranty, not even covered by the California emissions warranty.

The fuel level gauge is a coil of resistor wire and a wiper arm. As teh tank fills up, the wiper moves up on the resistor wire. You may have a spot on the resistor wire coil that the wiper no longer makes contact with due to corrosion or some kind of build up. Once it looses contact, it makes the tank look empty.

I had this same exact thing happen with my 2005 Xterra. My brother in law replaced the fuel level sending unit and it seemed to fix the gas gauge problem and remove the engine light. My problem now is that I have a hard time pumping gas. I guess the tank thinks it’s full and clicks off the pump several times while trying to fill up. I cannot seem to completely fill my tank and it takes about 20 minutes to do so. BIL said it might be a bent hose?? Any suggestions on something we might be able to check out before taking it to a mechanic?